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August 11, 2005

Weather balloons’ 1970s design caused climate spat

by Sam Savage

WASHINGTON (Reuters) - A dispute over whether global
warming is really happening may have been caused by the
placement of sensors on weather balloons when studies were done
in the 1970s, researchers said on Thursday.

Very few scientists now dispute that the Earth's
temperature is rising, and that this is caused by human
activity, including burning fossil fuels such as coal and oil.

But there have been some discrepancies that have troubled
experts. For instance, some measurements show that atmospheric
temperatures have been unchanged since the 1970s, while
temperatures at the Earth's surface are rising.

"Even though models predict a close link between
atmospheric and surface temperatures, there has been a large
difference in the actual measurements," said Steven Sherwood,
an associate professor of geology and geophysics at Yale
University in Connecticut, who led the study.

"This has muddied the interpretation of reported warming."

Working with a team at the National Oceanic and Atmospheric
Administration, Sherwood and colleagues said they found the key
to the differences lay in where the sensors were placed on
equipment.

With exposed sensors used in earlier designs, measurements
taken in daylight read too warm. Later equipment reduced this
effect.

"It's like being outside on a hot day -- it feels hotter
when you are standing in the direct sun than when you are
standing in the shade," Sherwood said in a statement.

"We can't hang our hats on the old balloon numbers."

Writing in the journal Science, Sherwood and colleagues
said this helps explain why temperatures in the troposphere --
the lower atmosphere -- appear not to have risen.

After taking this problem into account, they estimate there
has been an increase of 0.2 degree Celsius (0.36 degree F) in
the average global temperature per decade for the last thirty
years.

"Unfortunately, the warming is in an accelerating trend --
the climate has not yet caught up with what we've already put
into the atmosphere," Sherwood said. "There are steps we should
take, but it seems that shaking people out of complacency will
take a strong incentive."